430 ALTERNATING CURRENTS 



strontium salts a reddish tint and barium and titanium salts a 

 brilliant white light. 



As the electrode products are utilized in the arc, rapid consul np- 

 tion of the .electrodes results. This is accentuated by the fact 

 that air circulation is necessary to remove the white powder 

 deposited by the arc vapor. In the open type of lamp this 

 ventilation means a continuous supply of oxygen, resulting in 

 rapid consumption of the electrodes. The open type of lamp, 

 therefore, requires very long electrodes in order to obtain a 

 reasonable number of burning hours per trim. These electrodes 

 are so long that it is not practicable to place 

 them one above the other, so they are both fed 

 down from above and are placed at an angle, 

 as shown in Fig. 387. A small magnet M 

 blows the arc down. To increase the con- 

 ductance of the electrodes, a metallic wire is 

 usually run down their centers. This type of 

 lamp is very efficient, requiring only 0.43 watt 



FIG. 387. Short- i i n /^ 



burning flame arc. P er mean spherical candlepower. Owing to 

 the short life of the electrodes and the con- 

 sequent high cost of trimming, it cannot be profitably used 

 in this country for general illumination purposes. An un- 

 pleasant odor makes its use undesirable for interior illumination. 

 In this country its use is confined to outside display lighting. 

 Because of its high efficiency, this type is used extensively abroad 

 as the higher energy costs and the lower labor costs existing there 

 make its use economically desirable. 



To eliminate the short-burning feature of the flame arc 

 lamp and also the objection of the unpleasant fumes which 

 accompany its use, a long-burning type of lamp has been devel- 

 oped. The arc burns in a chamber, the air supply to which is 

 restricted. There is a large condensing chamber just above the 

 arc chamber. The hot gases rise and go into this condensing 

 chamber, where the white powder is condensed and deposited 

 against the comparatively cool surfaces of the chamber. The 

 gases are then allowed to re-enter the arc chamber. This re-utili- 

 zation of the same air prevents the access of a continuous supply 

 of oxygen and gives the lamp about 100 burning hours per trim. 

 Figure 388 shows the multiple lamp, together with the diagram of 



